Focus ring, substrate mounting table and plasma processing apparatus having same

ABSTRACT

A focus ring is placed on a substrate mounting table for mounting a target substrate thereon to surround the target substrate. The focus ring converges plasma on the target substrate when the target substrate is subjected to plasma processing. The focus ring is configured to create a temperature difference in its radial direction and over its full circumference during the plasma-processing of the target substrate. The focus ring also includes a radial outer region as a higher temperature region and a radial inner region as a lower temperature region. A groove is formed between the radial outer region and the radial inner region to extend over the full circumference of the focus ring.

CROSS-REFERENCE TO RELATED APPLICATIONS

This document claims priority to Japanese Patent Application No. 2008-187517, filed on Jul. 18, 2008, the entire content of which are hereby incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to a focus ring arranged in such a position as to surround a target substrate to be etched by plasma, a substrate mounting table for mounting a target substrate thereon and a plasma processing apparatus including the focus ring and the substrate mounting table.

BACKGROUND OF THE INVENTION

A parallel plate type plasma processing apparatus typically includes a lower electrode on which a target substrate is mounted, and an upper electrode arranged above the target substrate and provided with a plurality of gas injecting holes. An etching gas is injected through the gas injecting holes toward the whole target substrate and is converted into plasma, thereby simultaneously etching the entire surface of the substrate.

FIG. 11 is a view schematically showing a conventional plasma processing apparatus. The plasma processing apparatus includes a vacuum chamber 1 in which an upper electrode 21 having gas injecting holes and a lower electrode 2 serving as a substrate mounting table are placed one above the other. A focus ring 5 made of, e.g., silicon, is provided in such a fashion as to surround a target substrate (hereinafter referred to as a wafer) 15 mounted on the lower electrode 2.

The wafer 15 is electrostatically attracted by an electrostatic chuck 16. Within the electrostatic chuck 16, there is installed a flat internal electrode 17 to which a chuck voltage is fed from a power supply (not shown). A processing gas selected depending on the kind of processing is injected through the gas injecting holes of the upper electrode 21 toward the wafer 15. A vacuum pump (not shown) performs vacuum evacuation and maintains the pressure inside the chamber 1 at a predetermined level. Then, if a high-frequency voltage is applied from a high-frequency power supply 12 between the upper electrode 21 and the lower electrode 2, the processing gas is converted into plasma whereby the wafer 15 as a target substrate is subjected to specified processing, e.g., etching.

In the etching process, shapes such as trenches or holes are formed on the wafer in the vertical direction. For the vertical shape formation, a bias voltage is usually supplied to the wafer by applying high-frequency voltage in a relatively low frequency thereto. Electric fields perpendicular to the wafer surface are generated by the bias voltage. The vertical shape formation can be performed by the behavior of ions accelerated by the electric fields. Since the electric fields are distorted in an edge portion of the wafer, however, there is posed a problem that the bias voltage is not normally applied, causing shapes to be inclined.

As a result, it is sometimes the case that the devices obtained from a peripheral portion of the wafer 15 have low production yield. The low production yield due to non-uniform etching becomes significant as the diameter of the wafer 15 increases.

In order to cope with such a problem, the focus ring 5 of annular shape is arranged around the wafer 15 placed on the lower electrode 2 serving as a substrate mounting table. Thus the diameter of the wafer 15 in appearance is increased by the focus ring 5. Consequently, the peripheral portion of the wafer 15 is expanded to the peripheral portion of the focus ring 5, and the peripheral portion of the focus ring 5 can be regarded as the peripheral portion of the wafer 15. Accordingly, it is possible to make uniform the in-plane etching rate of the wafer 15. In addition, the following technique has been discussed as a method for making uniform the plasma state in the peripheral portion of the wafer 15.

Japanese Patent Laid-open Publication No. 2005-353812 discloses a temperature control mechanism for controlling the temperature of a focus ring to become higher than that of a wafer by 50° C. or more in order to optimize the plasma state, when plasma-processing the substrate mounted on a mounting table, and to carry out plasma processing on the substrate with increased in-plane uniformity. If the temperature of the focus ring is set higher than that of the wafer, the density of active species of plasma near the peripheral portion of the wafer tends to become smaller than the density of active species in the inner area of the wafer. This makes it possible to keep the density difference small, even though the density of active species near the peripheral portion of the wafer tends to become greater than the density of active species in the inner area of the wafer due to the exhaust gas flow.

The finding in the research made thus far by the present inventors reveals that the process characteristic difference in the wafer surface can be improved by cooling the focus ring heated by the impact of plasma ions to a temperature ranging, e.g., from the same temperature as that of the wafer to about 120° C. Especially, the present inventors have found that the afore-mentioned temperature control makes it possible to assure the uniformity of bottom critical dimension of holes and to prevent bowing from occurring in the outermost peripheral area, 10 mm wide, of the wafer, which has been problematic in the art. Accordingly, the present inventors have found that the afore-mentioned temperature control is highly effective in improving the process characteristic difference.

In the meantime, if the temperature of the focus ring is set substantially equal to that of the wafer, there may be a problem that the consumption rate of a photoresist film is increased and the selectivity of the photoresist film relative to an oxide film is reduced. As a result, it is impossible to etch the wafer in a desired depth.

SUMMARY OF THE INVENTION

In view of the above, the present invention provides a focus ring capable of improving the process characteristic difference of a wafer and capable of maintaining a photoresist film as a specified amount of residual film in the respective processes, thereby preventing the reduction of selectivity of the photoresist film relative to an oxide film.

The present invention also provides a substrate mounting table including the focus ring and a plasma processing apparatus including the substrate mounting table.

In accordance with an aspect of the present invention, there is provided a focus ring placed on a substrate mounting table for mounting a target substrate thereon to surround the target substrate. The focus ring converges plasma on the target substrate when the target substrate is subjected to plasma processing. The focus ring is also configured to create a temperature difference in its radial direction and over its full circumference during the plasma-processing of the target substrate.

The focus ring includes a radial outer region as a higher temperature region and a radial inner region as a lower temperature region.

A groove is formed between the radial outer region and the radial inner region to extend over the full circumference of the focus ring.

The groove extends inwards from an upper surface and/or a lower surface of the focus ring over the full circumference of the focus ring and is formed not to penetrate the focus ring.

The groove is formed to penetrate the focus ring so that the focus ring is divided into two bodies.

The groove is formed in a labyrinth shape.

A heat transfer unit is provided between the substrate mounting table and the radial inner region of the focus ring making contact with the substrate mounting table, and the lower temperature region is formed by heat exchange between the focus ring and the substrate mounting table.

A temperature increasing member is mounted on a part of the focus ring, and the high temperature region is formed as the temperature increasing member is heated by ion collision during the plasma processing.

A stepped portion is formed in a part of the focus ring, a temperature increasing member is mounted in the step portion to fill the stepped portion, and the higher temperature region is formed as the temperature increasing member is heated by ion collision during the plasma processing.

A substrate mounting table includes the focus ring.

The substrate mounting table further includes a cover ring arranged to surround the focus ring and a temperature increasing member annually mounted on an upper surface of the cover ring to extend over a full circumference of the cover ring.

A plasma processing apparatus includes: a processing chamber within which a processing gas is converted into plasma by high-frequency power; a substrate mounting table arranged within the processing chamber to mount a target substrate thereon, the target substrate being processed by the plasma; and a focus ring mounted on the substrate mounting table to surround the target substrate. Here, the focus ring is configured to create at least two regions of different temperatures in its radial direction and over its full circumference during the plasma-processing of the target substrate.

The focus ring includes: a radial outer region, as a higher temperature region, extending over a full circumference of the focus ring in between an outer circumference of the focus ring and a specified point radially inwardly spaced apart from the outer circumference; and a radial inner region, as a lower temperature region, extending over the full circumference of the focus ring in between the specified point and an inner circumference of the focus ring.

An annular groove is formed between the radial outer region and the radial inner region to extend over the full circumference of the focus ring.

The groove extends inwards from an upper surface and/or a lower surface of the focus ring over the full circumference of the focus ring and is formed not to penetrate the focus ring.

The groove is formed to penetrate the focus ring so that the focus ring is divided into two bodies.

The groove is formed in a labyrinth shape.

The plasma processing apparatus further includes a temperature increasing member mounted on a portion of the focus ring. Here, the high temperature region is formed as the temperature increasing member is heated by ion collision during the plasma processing.

A stepped portion is formed in a part of the focus ring and a temperature increasing member is mounted in the stepped portion to fill the stepped portion.

The plasma processing apparatus further includes a cover ring arranged to surround the focus ring and a temperature increasing member annularly mounted on an upper surface of the cover ring to extend over a full circumference of the cover ring.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects and features of the present invention will become apparent from the following description of embodiments, given in conjunction with the accompanying drawings, in which:

FIG. 1 shows a schematic configuration of a plasma processing apparatus in accordance with an embodiment of the present invention;

FIGS. 2A and 2B show a basic structure of a focus ring in accordance with an embodiment of the present invention;

FIGS. 3A and 3B show examples of the focus ring in which different temperature regions are formed;

FIG. 4 shows another example in which the focus ring is of a two-body type;

FIGS. 5A and 5B show other examples of the focus ring in which a groove is formed to extend through the focus ring;

FIG. 6 shows still another example of the focus ring in which a hot portion is provided with a heater and a groove;

FIG. 7 shows still another example of the focus ring in which two electrostatic chucks are independently provided under the focus ring;

FIGS. 8A and 8B show still other examples of the focus ring in which the hot portion is formed independently of the focus ring;

FIGS. 9A and 9B are graphs representing the etching rate of an oxide film and the etching rate of a photoresist, respectively, obtained in the comparative experiments of the present focus ring and the conventional focus ring;

FIGS. 10A and 10B are graphs representing a relationship between a wafer position and a bottom critical dimension and a relationship between a wafer position and an amount of residual photoresist; and

FIG. 11 schematically shows a conventional plasma processing apparatus.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, a plasma processing apparatus in accordance with an embodiment of the present invention will be described as a plasma etching apparatus in detail with reference to the accompanying drawings. However, the present invention shall not be limited to the embodiment.

FIG. 1 is a view showing the schematic configuration of a plasma processing apparatus in accordance with one embodiment of the present invention. Referring to FIG. 1, the plasma processing apparatus includes a chamber 1 made of, e.g., aluminum, stainless steel or the like. The chamber 1 has a hermetically sealable cylinder shape and remains electrically grounded.

In the chamber 1, a substrate mounting table (hereinafter referred to as a susceptor) 2 is placed to mount a target substrate, e.g., a wafer 15, thereon. The susceptor 2 shown in FIG. 1 is used as a heat exchange plate that controls the temperature of the wafer 15 by making contact with the wafer 15 and performing heat exchange therewith. The susceptor 2 is made of a material having good electric and thermal conductivity such as aluminum or the like, and serves as a lower electrode.

The susceptor 2 is supported by a tubular holder 3 made of an insulating material such as ceramic or the like. The tubular holder 3 is supported by a tubular support portion 4 of the chamber 1. A focus ring 5 made of silicon or the like is arranged on the upper surface of the tubular holder portion 3 so as to annularly surround the upper surface of the susceptor 2.

An annular exhaust path 6 is formed between the side wall and the tubular support portion 4 of the chamber 1. An annular baffle plate 7 is attached to the entrance or an intermediate area in the exhaust path 6. The bottom of the exhaust path 6 connected to an exhaust device 9 via an exhaust pipe 8. The exhaust device 9 includes a vacuum pump to evacuate the inner space of the chamber 1 to a predetermined degree of vacuum. Attached to the side wall of the chamber 1 is a gate valve 11 for opening and closing a gateway 10 through which the wafer 15 is loaded or unloaded.

A high-frequency power supply 12 for generating plasma is electrically connected to the susceptor 2 via a matching unit 13 and a power feeding rod 14. The high-frequency power supply 12 supplies electric power of relatively low frequency, e.g., 2 MHz, to the susceptor 2 serving as a lower electrode.

In a ceiling portion of the chamber 1, an upper electrode 21 is placed opposite to the lower electrode, i.e., the susceptor 2. The upper electrode 21 is formed into a hollow disk shape and has a plurality of gas injecting holes 22 on its lower surface. Thus the upper electrode 21 forms a shower head. An etching gas supplied from a processing gas supply unit is introduced into a cavity portion of the upper electrode 21 via a gas inlet line 23. The etching gas in the cavity portion is uniformly injected into the chamber 1 through the gas injecting holes 22.

An electrostatic chuck 16 made of a dielectric material such as ceramic or the like is placed on the upper surface of the susceptor 2 to hold the wafer 15 with an electrostatic force. An inner electrode 17 made of a conductive film, e.g., a copper film or a tungsten film, is buried in the electrostatic chuck 16.

A direct current power supply (not shown) of high voltage, e.g., 2500 V or 3000 V, is electrically connected to the inner electrode 17 through a switch. If a direct current voltage is applied to the inner electrode 17, the wafer 15 is attracted to and held by the electrostatic chuck 16 under the action of a Coulomb force or a Johnson-Rahbek force.

A heat medium (or fluid) flow path 18 is provided in the susceptor 2. A heat medium, e.g., hot water or cold water, of predetermined temperature is supplied from a temperature control unit (not shown) to the heat medium flow path 18 via a pipeline 20.

A heat transfer gas, e.g., He gas, is supplied from a heat transfer gas supply unit (not shown) to between the electrostatic chuck 16 and the back surface of the wafer 15 through a gas supply pipe 24. The heat transfer gas assures accelerated heat transfer between the electrostatic chuck 16, i.e., the susceptor 2 and the wafer 15.

FIGS. 2A and 2B show the basic structure of the focus ring 5 in accordance with an embodiment of the present invention. The focus ring 5 has two regions, namely a cold portion 50 a and a hot portion 50 b.

The temperature of the focus ring 5 is set as follows. For example, the temperature of the cold portion 50 a is set within a range of ±50° C. of the temperature of the wafer 15, and the temperature of the hot portion 50 b is set 100° C. greater than the temperature of the wafer 15. Alternatively, the temperature of the cold portion 50 a may be set within a range from 0° C. to 100° C., and the temperature of the hot portion 50 b may be set greater than the temperature of the cold portion 50 a but within the upper limit of 600° C. Referring to FIG. 2A, the two temperature regions, i.e., the cold portion 50 a (low temperature region) and the hot portion 50 b (high temperature region), are formed during the plasma processing. The focus ring 5 may be configured to have three or more temperature regions or to have a temperature gradient.

The temperatures of the cold portion 50 a and the hot portion 50 b can be set by, e.g., burying a heater and a coolant gas pipe in the respective regions, the temperatures of the heater and the coolant gas pipe being controllable independently of each other. Alternatively, the hot portion 50 b and the cold portion 50 a may be configured to have different temperatures by placing heat transfer sheets 101 having different heat conductivity between the electrostatic chuck 16 and the focus ring 5.

FIG. 2B shows an instance where the hot portion 50 b and the cold portion 50 a are formed along the full circumference of the focus ring 5. In FIG. 2B, the hot portion 50 b is annularly formed to have a width equal to one thirds of the total width of the focus ring 5, and the cold portion 50 a is annularly formed inwards of the hot portion 50 b to have a width equal to two thirds of the total width of the focus ring 5.

EXAMPLES

FIGS. 3A and 3B show the structures of the focus ring 5, as examples of the embodiment of the present invention in which two regions of different temperatures are formed in the focus ring 5 during the plasma processing. As shown in FIGS. 3A and 3B, each of the focus rings 5 has a structure in which an annular groove is formed extending along the full circumference of the focus ring 5 at a position radially distant about one thirds of the total width of the focus ring 5 from the outer circumference of the focus ring 5.

Specifically, FIG. 3A shows an instance where a groove 100 a is formed in the surface of the focus ring 5 making contact with the electrostatic chuck 16 (namely, in the lower surface of the focus ring 5). FIG. 3B shows an instance where a groove 100 b is formed in the upper surface of the focus ring 5. By forming the groove 100 a or 100 b, it is possible to reduce the heat transfer rate between the cold portion and the hot portion.

A heat transfer sheet 101 is provided below the cold portion to improve heat exchange between the cold portion and the susceptor 2. The focus ring 5 is heated as a result of the collision of ions generated by plasma. Unlike the cold portion, the hot portion is not cooled because no heat transfer sheet 101 is placed below the hot portion.

Furthermore, the heat exchange is not sufficiently implemented between the hot portion and the cold portion due to the hollow groove 100 a or 100 b therebetween. Thanks to such features, it is possible to create the two temperature regions, i.e., the cold portion and the hot portion, in the focus ring 5 during the plasma processing. The groove 100 a or 100 b can be formed by a mechanical work using a laser or a cutter or a chemical work such as etching or the like. Although the groove 100 a or 100 b is left hollow, the groove 100 a or 100 b may be filled with a medium of low heat transfer rate or a medium of specified heat transfer rate depending on the process characteristics.

FIG. 4 shows another example in which the focus ring 5 is of a two-body type. The focus ring 5 has an annular stepped portion formed along its full outer circumference, the stepped portion having a width equal to about one thirds of the total width of the focus ring 5. It is preferred that the stepped portion has a height equal to about one half of the thickness of the focus ring 5, e.g., about 1 to 3 mm.

A temperature increasing member 102, which has a shape following that of the stepped portion, is mounted on the stepped portion. With such a structure of the focus ring 5, the cold portion has a predetermined temperature by the heat exchange with the susceptor 2 in the plasma processing of the wafer. Since the temperature increasing member 102 is merely mounted on the stepped portion in the hot portion, vacuum heat insulation is provided between the temperature increasing member 102 and the focus ring 5. The temperature increasing member 102 hardly performs heat exchange with the focus ring 5. Further as in the examples shown in FIGS. 3A and 3B, the heat transfer sheet 101 is not placed in the hot portion. As a result, the hot portion of the focus ring 5 has a temperature higher than that of the cold portion. The temperature increasing member 102 is heated to a high temperature by the collision of ions generated by plasma. With this structure of the focus ring 5, the two regions of different temperatures, i.e., the hot portion and the cold portion can be formed in the focus ring 5 during the plasma processing.

FIGS. 5A and 5B show other examples in which a groove is formed to extend through the focus ring 5 between the upper and lower surfaces thereof. FIG. 5A shows an instance where a groove 100 c extends straightly through the focus ring 5, and FIG. 5B shows an instance where a groove 100 d extends in a labyrinth shape through the focus ring 5. With the groove 100 c straightly extending through the focus ring 5 between the upper and lower surfaces thereof as shown in FIG. 5A, it is possible to more efficiently prevent heat exchange between the hot portion and the cold portion. In case of such a straight dividing structure, however, plasma may pass through the groove 100 c and may collide against the electrostatic chuck, possibly causing damage to the electrostatic chuck and other parts. If the focus ring 5 is divided by using the groove 100 d of labyrinth shape as shown in FIG. 5B, it is possible to prevent the electrostatic chuck and other parts from being damaged by the collision of plasma.

FIG. 6 shows still another example of the focus ring 5 in which heaters 103 a and 103 b are provided in the hot portion of the same structure as shown in FIG. 3A. In addition, a groove 100 f is formed between the heaters 103 a and 103 b and a groove 100 e is formed radially inwards of the heater 103 b. By providing the heaters 103 a and 103 b in the hot portion, it is possible to more accurately control the temperature of the hot portion. In general, by providing the heaters 103 a and 103 b and the grooves 100 f and 100 e in plural numbers, it is possible to create a temperature gradient so that the temperature of the focus ring 5 can be increased in its outer direction.

FIG. 7 shows a case where two electrostatic chucks are independently provided under the focus ring 5. Substrate attracting electrodes 104 a and 104 b and heat transfer gas pipelines (not shown) are provided in the hot portion and the cold portion, which makes it possible to more efficiently control the temperatures of the hot portion and the cold portion. Although the substrate attracting electrodes 104 a and 104 b are provided independently of each other in FIG. 7, they may be consolidated into a single electrode while independently arranging the heat transfer gas pipelines. As a further alternative, the substrate attracting electrodes 104 a and 104 b and the heat transfer gas pipelines (not shown) may be installed only in the cold portion.

FIGS. 8A and 8B show cases where the hot portion is provided independently of the focus ring 5. In particular, FIG. 8A shows an instance where a hot portion 105 having a T-shaped cross-section is provided on the upper surface of the outer area of the focus ring 5, the hot portion 105 extending along the full circumference of the focus ring 5. In this case, it is preferred that the T-shaped hot portion 105 has a height of about 1 to 5 mm. Although the hot portion 105 has a width equal to about one thirds of the total width of the focus ring 5 in FIG. 8A, it is desirable to change the width of the hot portion 105 depending on the process types. With such a configuration, it is possible to optimize the plasma state by using the influence of the temperature of the side surface as well as the upper surface of the T-shaped hot portion 105. Alternatively, the hot portion may be formed into an L-shape or an inverted L-shape instead of the T-shape. By doing so, it is possible to reduce the contact area between the hot portion and the cooled focus ring 5 and to rapidly increase the temperature of the hot portion.

FIG. 8B shows an instance where a hot portion 106 is provided on the cover ring 25 of the focus ring 5 along its full circumference. It is preferred that the hot portion 106 has a height of about 1 to 5 mm. With this configuration, the temperature of the side surface as well as the upper surface of the hot portion 106 can be used to optimize the plasma state, similar to that of FIG. 8A.

(Comparative Experiment)

FIGS. 9A and 9B are graphs representing the etching rates of blanket wafers having a diameter of 300 mm, which were obtained in the comparative experiments for the present focus ring shown in FIG. 4 and the conventional focus ring. The comparative experiment results of the etching rate of an oxide film are shown in FIG. 9A, and the comparative experiment results of the etching rate of a photoresist are shown in FIG. 9B. The zero point in the horizontal axis denotes the center point of the blanket wafer, and the ±150 points denote the opposite ends of the blanket wafer. The vertical axis in FIG. 9A refers to the etching rate of an oxide film, which is standardized based on the etching rate at the center point of the blanket wafer. If the etching rate at a specified position is greater than that of the center point, the corresponding value becomes greater than 1 (one). If the etching rate at a specified position is smaller than that of the center point, the corresponding value becomes smaller than 1 (one).

In FIGS. 9A and 9B, “STD FRØ360” refers to a curve in a condition where the temperature of the focus ring (with a width of 30 mm) for the 300 mm wafer is controlled to become substantially equal to the wafer temperature during the plasma processing. “FRØ340” refers to a curve in a condition where the temperature increasing member 102 having a width of 10 mm is mounted at a position radially outwardly distant 170 mm from the center point (zero point) of the blanket wafer as illustrated in FIG. 4, and the temperature of the cold portion is controlled to become substantially equal to that of the wafer.

“FRØ330” refers to a curve in a condition where the temperature increasing member 102 having a width of 15 mm is mounted at a position radially outwardly distant 165 mm from the center point (zero point) of the blanket wafer as illustrated in FIG. 4, and the temperature of the cold portion is controlled to become substantially equal to that of the wafer.

“FRØ320” refers to a curve in a condition where the temperature increasing member 102 having a width of 20 mm is mounted at a position radially outwardly distant 160 mm from the center point (zero point) of the blanket wafer as illustrated in FIG. 4, and the temperature of the cold portion is controlled to become substantially equal to that of the wafer. These experiments were performed under the common environmental conditions: the flow rates of etching gases, CuF₆/Ar/O₂, of 60/400/55 sccm; the gas pressure of 15 mTorr; and the HF and LF power of 2700 W/4500 W. The temperature of the hot portion of the focus ring is set equal to about 550° C., and the temperature of the cold portion set equal to about 100° C. The estimated temperature of the wafer is about 80° C.

In the case of the etching rate of the oxide film shown in FIG. 9A, the curve “STD FRØ360” indicates that the etching rate becomes greater at the position radially inwardly distant 50 mm from the outer circumference of the wafer than at the center area. The etching rate is sharply increased at the position radially inwardly distant 10 mm from the outer circumference of the wafer. The etching rate in the outer circumference of the wafer is about 15% greater than that at the center area. In contrast, in the case of the focus rings according to the embodiment of the present invention, all curves indicate that the increase in the etching rate is restricted as compared to the curve “STD FRØ360”. Especially, the curve “FRØ320” shows the most effect in the process of the afore-mentioned conditions.

In the case of the etching rate of the photoresist shown in FIG. 9B, the curve “STD FRØ360” indicates that the etching rate begins to increase at the position radially inwardly distant 50 mm from the outer circumference of the wafer, and the etching rate in the outer circumference of the wafer becomes two or more times greater than at the center area. In contrast, as compared to the curve “STD FRØ360”, in the case of the focus rings according to the embodiment of the present invention, all curves indicate that the etching rate can be maintained in a low level in the section between the outer circumference of the wafer and the position radially inwardly distant 50 mm from the outer circumference. Especially, the curve “FRØ330” indicates that the etching rate is maintained substantially the same in the outer circumference and the center area of the wafer.

In the case of the curve “FRØ320”, the etching rate tends to become smaller from the center area toward the outer circumference of the wafer. The test results show that the etching rates of an oxide film and a photoresist can be freely controlled by creating a temperature difference in the surface of the focus ring and controlling the temperature difference.

FIG. 10A is a graph representing the relationship between a position on the wafer having a diameter of 300 mm (whose center point is indicated by “0”) and the bottom critical dimension of a hole, wherein the wafer has an oxide film and a resist pattern formed on the oxide film. In FIG. 10A, STD FRØ360, FRØ340 and FRØ320 refer to curves corresponding to the same focus rings as mentioned in FIGS. 9A and 9B.

As shown in FIG. 10A, in the case of the curve “STD FRØ360”, the bottom critical dimension of a hole shows no great difference between the center area and the outer circumference of the wafer, and little difference is made in the process characteristics. The curve “FRØ340” also shows substantially identical tendency. That is to say, little difference in the process characteristics is made between the center area and the outer circumference of the wafer. In the case of the curve “STD FRØ320”, the bottom critical dimension of a hole is decreased by 20 nm or more from the position distant 10 mm from the outer circumference of the wafer and is sharply reduced in the outer circumference of the wafer.

FIG. 10B is a graph representing the relationship between a position on the wafer (whose center point is indicated by “0”) and the amount of residual photoresist on the oxide film. The wafer is the same one as illustrated in FIG. 10A. In the case of the curve “STD FRØ360”, the amount of residual photoresist is sharply decreased from the 100 mm position toward the outer circumference of the wafer. In contrast, in the case of the curve “STD FRØ340”, it is possible to maintain, by 50% or less, the decrease in the amount of residual photoresist occurring from the 120 mm position toward the outer circumference of the wafer. In the case of the curve “STD FRØ320”, the amount of residual photoresist tends to be increased from a position distant 30 mm from the outer circumference of the wafer.

These experiment results demonstrate that it is possible to suitably maintain the bottom critical dimension and the amount of residual photoresist by creating a temperature difference in the surface of the focus ring. In particular, by forming the regions of different temperatures in the surface of the focus ring, it is possible to secure the uniformity in the bottom critical dimension and to improve the difference in the process characteristics. In addition, the present invention is capable of solving the mutually contradictory problems inherent in the prior art that the secured uniformity in the bottom critical dimension causes the consumption rate of the photoresist film to be increased, consequently making it impossible to etch the wafer up to a specified depth and reducing the selectivity of the photoresist film relative to the oxide film. It is also found that bowing can be prevented by creating a temperature difference in the surface of the focus ring.

With the embodiments of the present invention, it becomes possible to provide a focus ring capable of improving the process characteristic difference of a wafer and capable of maintaining a photoresist film as a specified amount of residual film in the respective processes, thereby preventing the reduction of selectivity of the photoresist film relative to an oxide film. It is also possible to provide a substrate mounting table including the focus ring and a plasma processing apparatus including the substrate mounting table.

While the invention has been shown and described with respect to the embodiments, it will be understood by those skilled in the art that various changes and modification may be made without departing from the scope of the invention as defined in the following claims. 

1. A focus ring placed on a substrate mounting table for mounting a target substrate thereon to surround the target substrate, the focus ring converging plasma on the target substrate when the target substrate is subjected to plasma processing, wherein the focus ring is configured to create a temperature difference in its radial direction and over its full circumference during the plasma-processing of the target substrate.
 2. The focus ring of claim 1, which comprises a radial outer region as a higher temperature region and a radial inner region as a lower temperature region.
 3. The focus ring of claim 2, wherein a groove is formed between the radial outer region and the radial inner region to extend over the full circumference of the focus ring.
 4. The focus ring of claim 3, wherein the groove extends inwards from an upper surface and/or a lower surface of the focus ring over the full circumference of the focus ring and is formed not to penetrate the focus ring.
 5. The focus ring of claim 3, wherein the groove is formed to penetrate the focus ring so that the focus ring is divided into two bodies.
 6. The focus ring of claim 5, wherein the groove is formed in a labyrinth shape.
 7. The focus ring of claim 2, wherein a heat transfer unit is provided between the substrate mounting table and the radial inner region of the focus ring making contact with the substrate mounting table, and the lower temperature region is formed by heat exchange between the focus ring and the substrate mounting table.
 8. The focus ring of claim 2, wherein a temperature increasing member is mounted on a part of the focus ring, and the high temperature region is formed as the temperature increasing member is heated by ion collision during the plasma processing.
 9. The focus ring of claim 2, wherein a stepped portion is formed in a part of the focus ring, a temperature increasing member is mounted in the step portion to fill the stepped portion, and the higher temperature region is formed as the temperature increasing member is heated by ion collision during the plasma processing.
 10. A substrate mounting table comprising the focus ring of claim
 1. 11. The substrate mounting table of claim 10, further comprising a cover ring arranged to surround the focus ring and a temperature increasing member annually mounted on an upper surface of the cover ring to extend over a full circumference of the cover ring.
 12. A plasma processing apparatus comprising: a processing chamber within which a processing gas is converted into plasma by high-frequency power; a substrate mounting table arranged within the processing chamber to mount a target substrate thereon, the target substrate being processed by the plasma; and a focus ring mounted on the substrate mounting table to surround the target substrate, wherein the focus ring is configured to create at least two regions of different temperatures in its radial direction and over its full circumference during the plasma-processing of the target substrate.
 13. The apparatus of claim 12, wherein the focus ring includes: a radial outer region, as a higher temperature region, extending over a full circumference of the focus ring in between an outer circumference of the focus ring and a specified point radially inwardly spaced apart from the outer circumference; and a radial inner region, as a lower temperature region, extending over the full circumference of the focus ring in between the specified point and an inner circumference of the focus ring.
 14. The apparatus of claim 13, wherein an annular groove is formed between the radial outer region and the radial inner region to extend over the full circumference of the focus ring.
 15. The apparatus of claim 14, wherein the groove extends inwards from an upper surface and/or a lower surface of the focus ring over the full circumference of the focus ring and is formed not to penetrate the focus ring.
 16. The apparatus of claim 14, wherein the groove is formed to penetrate the focus ring so that the focus ring is divided into two bodies.
 17. The apparatus of claim 16, wherein the groove is formed in a labyrinth shape.
 18. The apparatus of claim 13, further comprising a temperature increasing member mounted on a portion of the focus ring, wherein the high temperature region is formed as the temperature increasing member is heated by ion collision during the plasma processing.
 19. The apparatus of claim 12, wherein a stepped portion is formed in a part of the focus ring and a temperature increasing member is mounted in the stepped portion to fill the stepped portion.
 20. The apparatus of claim 12, further comprising a cover ring arranged to surround the focus ring and a temperature increasing member annularly mounted on an upper surface of the cover ring to extend over a full circumference of the cover ring. 